This invention relates to a system of irrigation which allows the watering of a large land area to be automatically and constantly monitored and controlled. Hitherto the control of irrigation has been a matter for visual inspection and the subsequent interruption of the water supply from which irrigation is taking place; i.e. a flood gate, turn cock or spray system. This process is obviously time consuming and unreliable, requires the employment of intermittent labour and is very much subject to human error.